Injection molding machines of the type in which the invention pertains generally comprise an elongated feedscrew which rotates and reciprocates axially in the cylindrical bore of an elongated heated barrel for moving heated plastic material from an inlet end to the outlet end where it is injected from a distribution chamber through a nozzle and into a mold cavity. The flow of the heated plastic into the distribution chamber for subsequent discharge through the nozzle is controlled by a check valve assembly which includes a movable check ring for regulating the flow of heated material past a front seat and into the distribution chamber. The check ring moves rearwardly into sealing engagement with a rear seat portion of the check valve assembly in response to back pressure created by the plastic trapped in a filled distribution chamber during the injection molding cycle. When the back pressure is released upon filling of the mold cavity, the check ring moves away from the rear valve seat allowing for the continued flow of the melted plastic material through the check valve assembly and into the distribution chamber for subsequent discharge through the nozzle and into the mold cavity during the next injection cycle. The heated material is in the form of a cylindrical sleeve as it moves through an annular flow gap formed by the internal periphery of the check ring.
A common problem with such types of check valve assemblies having the movable check ring is that the cylindrical sleeve of material flowing pass the check valve is restricted when flowing pass the front valve seat due to the size and configuration of the opening provided in the front seat.
These prior front seat openings usually consist of a plurality of ports or arcuate groove sections arranged in a segmented circular fashion at the end of the annular flow gap whereby the sleeve of material continues to move axially through the plural openings for subsequent splitting and distribution through flutes or other openings prior to entering the distribution chamber. Since the total volume of the front valve seat openings is not equal to the cross sectional volume of the incoming sleeve of material, portions of the moving sleeve of material are blocked requiring the material to be channeled about such obstructions in order to enter the flute areas. This restricted flow reduces the amount of material able to flow into the mold cavity within a predetermined period of time which increases the injection cycle time which determines the capacity and operational speed of the injection molding machine. Also a mechanical shearing action is exerted on portions of the moving sleeve of material as it passes the obstructions and creates frictional heat at the area of the front valve seat which increases the temperature of the moving material. Such heat effects the control temperature of the plastic material which can be critical for certain heat sensitive materials being injection molded.
Examples of prior art injection molding machines having valve assemblies somewhat similar in structure and operation on which the subject invention is an improvement thereon are shown in U.S. Pat. Nos. 2,940,123; 3,319,299; 3,335,461; 3,590,439; 4,062,479; 4,105,147; 4,349,044; and 4,394,117. Accordingly, the need has existed for an improved check valve assembly which provides for the unrestricted flow of a cylindrical sleeve of material past the front valve seat and into the distribution chamber of an injection molding machine. There is no known check valve assembly of which I am aware having an improved front valve seat therein which enables such results to be achieved other than my invention described in detail below.